Graphite crystal has a hexagonal network plane layered structure composed of carbon elements. The carbon atoms on the layer plane are bound by strong covalent bonds, while the layers are bound by van der Waals force. The binding is very weak, and the distance between layers is large. Therefore, under appropriate conditions, acid, alkali gold, salt and other chemical substances can be inserted into the graphite layers, It combines with carbon atoms to form a new chemical phase Graphite Intercalation on Compounds (GIC). When heated to an appropriate temperature, this interlayer compound can instantly and rapidly decompose, generating a large amount of gas, which makes graphite expand along the axis into a new worm like material, namely expanded graphite. This unexpanded graphite interlayer compound is expandable graphite.
Expandable graphite was first discovered by Schaufautl, a German. In 1841, Schaufautl soaked natural graphite in a mixture of concentrated HNO3 and concentrated H2SO4, and took it out for drying several hours later. It was found that the graphite had expanded. United Carbide first applied for a patent for the manufacturing technology of expandable graphite in 1963 and carried out industrial production in 1968.
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